1. Field Of The Invention
The present invention relates to a method of preparing composite structures comprising a layer of flexible polyurethane foam bonded to a substrate by means of heat and to the resulting composites. More particularly, the invention relates to the use of polyurethane foams prepared from graft polyols in the preparation of heat sealable composites.
2. Prior Art
Several heat sealing methods are known in the art for laminating plastic sheets together, which methods preclude the use of an adhesive. One such method, which is particularly desirable in view of its speed and ease of application, is the so-called dielectric heat sealing method. This comprises pressing the layers to be adhered together between two surfaces while applying a high-frequency voltage thereto. The heat generated by this voltage fuses the layers at the inter-face, and upon cooling and solidification of the fused inter-face, the layers become permanently bonded together. This and other heat sealing methods in general have been successfully employed in laminating polyester polyol but not polyether polyol polyurethane foam to other materials. In the case of polyurethane foam of the polyether type, difficulty was encountered in permanently heat sealing them to other materials.
Previous attempts to overcome this difficulty have included employing certain low molecular weight polyols in the foam preparation (U.S. Pat. No. 3,205,120); using a particular organic polyisocyanate in the foam preparation (U.S. Pat. No. 3,497,116); incorporating conductive particles in the foam (U.S. Pat. No. 3,499,848); applying a thin layer of a dipolar material to the foam surface before sealing it to another plastic sheet (U.S. Pat. No. 2,859,153); incorporating highly polar, reactive hydrogen-containing compounds in the foam-forming reaction mixture (U.S. Pat. No. 3,674,718); and employing various vinyl polymer fillers as one component of the urethane reaction mixture.